Door ajar detection and recovery for a wireless door sensor

ABSTRACT

A refrigerated container system is described that includes a wireless personal area network (WPAN) including a plurality of wireless sensor nodes and a coordinator node through which the sensors provide sensor data to a controller for the refrigerated container system. The wireless sensors and the coordinator incorporate a variety of features that ensure efficient utilization of battery life by preventing unintended pairing of sensors with other WPANs and excessive sensor signal processing arising from door chatter. Finally, pairing is performed without pressing a button on the wireless door sensor. Instead, the sensor&#39;s magnetic reed switch is enlisted to detect swiping of a magnet by a user to enter a pairing mode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority benefit of Johnson et al., U.S.Provisional Patent Application Ser. No. 61/613,963, filed on Mar. 21,2012, entitled “Refrigerated Container System Including Wireless SensorPersonal Area Network,” the contents of which are expressly incorporatedherein by reference in their entirety, including any references therein.

This application relates to Johnson et al., U.S. patent application Ser.No. 13/709,380, filed on Dec. 7, 2012, entitled “A Means for Pairing aHermetically Sealed Wireless Device,” the contents of which areexpressly incorporated herein by reference in their entirety, includingany references therein.

This application relates to Johnson et al., U.S. patent application Ser.No. 13/709,356, filed on Dec. 7, 2012, entitled “Wireless Device PairingRecovery,” the contents of which are expressly incorporated herein byreference in their entirety, including any references therein.

This application relates to Johnson et al., U.S. patent application Ser.No. 13/709,371, filed on Dec. 7, 2012, entitled “RF4CE for Automotiveand Industrial Environments,” the contents of which are expresslyincorporated herein by reference in their entirety, including anyreferences therein.

This application relates to Johnson et al., U.S. patent application Ser.No. 13/709,348, filed on Dec. 7, 2012, entitled “,” the contents ofwhich are expressly incorporated herein by reference in their entirety,including any references therein.

TECHNICAL FIELD

This patent disclosure relates generally to a transportable refrigeratedcontainer system (also known as a “reefer”), and more particularly, arefrigerated container system including a controller and a set ofwireless sensors communicating over a short range wireless network.

BACKGROUND

Generally, refrigerated container systems facilitate transporting cargoin a cooled state to maintain a particular desired quality while thecargo is transported to intended destinations. The cargo is transported,stored, or otherwise supported within a cargo space of the transportcontainer, and is maintained at a desired temperature within the cargospace using a transport refrigeration system.

A control unit typically provides automated monitoring and control ofthe status and operation of a refrigerated container system. Forexample, the control unit regulates the temperature of a cargo spacewithin the container by turning a refrigeration unit on/off based onsensed temperature and a setpoint temperature. The control unit is alsocapable of sensing other conditions relating to the cargo space of therefrigerated container system. One such condition is the open/closedstate of one or more doors provided on the refrigerated container foraccessing the cargo.

The desirability of having a network of sensors in a refrigeratedcontainer system, both temperature and door state, is clear. However,incorporating wireless door sensors into control networks forrefrigerated containers presents unique challenges that are describedand addressed herein.

SUMMARY OF THE INVENTION

The disclosure describes several aspects of managing a wireless personalarea network (WPAN) incorporated within a refrigerated container system.

In a first aspect, a method, performed by a wireless sensor node, isdescribed for pairing a wireless sensor including a switch with acoordinator in a wireless personal area network. The method includesfirst sensing actuation of the switch according to a first actuationsequence timing requirement. The first sensing must then be followed bysecond sensing no actuation of the switch, for a first designatedwaiting period commencing after the first sensing has ended and thenthird sensing actuation of the switch according to a second actuationsequence timing requirement after the second sensing. The wirelesssensor enters a pairing mode with the coordinator only after completingat least the third sensing step.

In a second aspect, a method, performed by a wireless sensor node, isdescribed for actively purging, without operator intervention,coordinator entries from a pairing table for a wireless sensorincorporated into a wireless personal area network. The method comprisesregistering a failure by the wireless sensor to connect to a firstcoordinator identified in the pairing table. A second coordinator isidentified in the pairing table. A determination is then made that thewireless sensor has repeatedly failed to connect to the coordinator aspecified number of times over a period of time. Then the firstcoordinator is purged from the pairing table in response to theidentifying and determining steps.

In a third aspect, a mobile container system is describes that includesa cargo containment space. The system further includes a controllermonitors and maintains conditions of a space within the cargo container.The container system also includes a wireless personal area network(WPAN) comprising: a set of wireless sensor nodes that generate, for thecontroller, status information relating to the cargo container, and acoordinator node that receives, on behalf of the controller, the statusinformation via wireless connections to paired ones of the set of sensornodes. The WPAN enables the set of sensors to provide the statusinformation for use by the controller via the coordinator node.

In a fourth aspect, a method is described for managing a wireless doorsensor to avoid excessive sensor signal processing arising from achattering door sensor signal stream. The method comprises detecting, bythe wireless door sensor, a specified number of door transitions withina specified time period. In response to said detecting the followingfurther steps are performed: (1) disabling a door signal transitionevent processing routine; (2) enabling a timer-based door sensor signalprocessing routine, wherein the timer-based routine reads a door sensorsignal status regardless of whether a door signal transition hasoccurred, and (3) re-enabling the door signal transition eventprocessing routine in response to reading a same value for the doorsensor signal status multiple times over a time duration. The multiplereadings indicate the door position has stabilized.

In a fifth aspect, a method, performed by a coordinator node, isdescribed for preventing inadvertent pairing of a sensor device with thecoordinator in a WPAN network incorporated into a refrigerated containersystem. The method comprises: (1) extracting a property value from apairing request message provided by the sensor device to thecoordinator; (2) comparing the property value to expected propertyvalues for sensor devices in the wireless personal area network; and (3)conditionally allowing, by the coordinator, pairing with the sensorbased upon the comparing step.

BRIEF DESCRIPTION OF THE DRAWINGS

While the appended claims set forth the features of the presentinvention with particularity, the invention and its advantages are bestunderstood from the following detailed description taken in conjunctionwith the accompanying drawings, of which:

FIG. 1, is a side view of a trailer having an integrated refrigerationsystem in accordance with the disclosure;

FIG. 2 is a schematic diagram of an exemplary wireless personal areanetwork (WPAN) for wireless communication between a controller and aplurality of wireless sensor-transmitters in accordance with thedisclosure;

FIG. 3 is an exemplary frame definition for messages transmitted bysensor-transmitters in accordance with the disclosure;

FIGS. 4A and 4B depict an exemplary door sensor module (4A) and magnet(4B) in accordance with the disclosure;

FIG. 5 is a sequence diagram summarizing stages for performing asequence of magnet swipes detected by a magnetically sensitivecomponent, such as a reed switch, to initiate pairing between a sensordevice and a coordinator in a WPAN in accordance with the disclosure;

FIG. 6 is a paired device registration table entry format in accordancewith the RF4CE specification;

FIG. 7A is a flowchart summarizing steps carried out in a device toremove erroneous pairing table entries in accordance with thedisclosure;

FIG. 7B summarizes a set of measures incorporated into pairing logicimplemented by a coordinator node to ensure against unintended/improperpairing with a sensor;

FIG. 7C is a flowchart summarizing steps carried out on a coordinatornode to ensure against unintended pairing with a wireless node;

FIGS. 8A and 8B are state diagrams representing the registered status ofa door sensor (open/closed) over time when the door is chattering; and

FIG. 9 is a flowchart summarizing a set of steps for selectivelydisabling/enabling a door sensor signal interrupt handling routine inresponse to door chatter condition detection.

DETAILED DESCRIPTION OF THE DRAWINGS

Turning initially to FIG. 1, a side view is provided of a trailer unit100 with a transport refrigeration system 110. The trailer unit 100 isinstalled on a frame 120 and has a plurality of side doors 112 and arear door 114. The transport refrigeration system 110 is installed on aside wall of the trailer unit 100. The transport refrigeration system110 is configured to transfer heat between an internal space 130 and theoutside environment.

It will be appreciated that the embodiments described herein are notlimited to trucks and trailer units. The embodiments described hereinare used in any other suitable temperature controlled container systems.The refrigeration system 110 is, for example, a vapor-compressor typerefrigeration system, or any other suitable refrigeration system.

The transport refrigeration system 110 includes a wireless communicationsystem 140 (see FIG. 2) and a fuel tank 145. The wireless communicationsystem 140, described herein below with reference to FIG. 2, includes acontroller (not shown), an antenna 150, and a plurality of wireless endnodes 155. As shown in FIG. 1, the wireless end nodes 155 include a doorsensor 155 a for each of the side doors 112 and the rear door 114, and afuel tank level sensor 155 b for the fuel tank 145. The wireless endnodes 155, in other systems, include other types of sensors such as, forexample, an air space temperature sensor, a humidity sensor, a cargotemperature sensor, accelerometer, etc. Also, the wireless end nodes 155are hermetically sealed to prevent water and contaminant ingress. Thewireless communication system 140 is configured to enable the wirelessend nodes 155 to communicate information regarding the monitored statusof the refrigerated container system, incorporated into the trailer unit100, to a controller unit (not shown) of the transport refrigerationsystem 110 for controlling the heating, ventilation and air conditioning(“HVAC”) of the internal space 130.

Turning to FIG. 2, the wireless communication system 140 incorporates,by way of example, an exemplary wireless personal area network (WPAN)for wireless communication between a controller and a plurality ofsensors including wireless transceivers. In the particular illustrativenetwork depicted in FIG. 2, a WPAN coordinator node 200 communicateswirelessly with a plurality of previously paired wireless sensor nodesincluding a fuel sensor 202, pallet temperature sensor 204, pallet loadsensor 206, humidity sensor 208, temperature sensor 210, side doorsensors 212, 214, and back door sensor 216.

By way of example, the WPAN coordinator node 200 includes, among otherthings, an external antenna to support sufficient communication rangefor communicating with remotely located sensor/transceivers in the WPANpositioned on a refrigerated transport container/vehicle such as the onedepicted in FIG. 1. The coordinator node 200 is also equipped with apairing mode button and status LEDs for pairing with and thereaftervisually indicating the status of paired sensor nodes within the WPAN.

The sensor nodes are generally equipped with function-specific sensorhardware, a data interface between the sensor and a controller/processorwithin the sensor module, and a transceiver for communicating statusinformation with the coordinator node 200 (after pairing). A particularexample of a door sensor assembly is described herein below withreference to FIGS. 4A and 4B.

The coordinator node 200 is connected via a wired interface to arefrigerated container controller 220. The refrigerated containercontroller 220 is communicatively coupled to a Wi-Fi modem/transceiver230. The Wi-Fi modem/transceiver 230 provides, by way of example, awireless connection to the Internet through which the refrigeratedcontainer controller 220 communicates with a variety of resources. TheWPAN depicted in FIG. 3 also includes a wirelessly linked display 240providing in-cab information relating to the status of the refrigeratedcontainer system based upon status information provided by thecoordinator node 200. The coordinator node 200, incorporating RF4CEcommunication protocols (see below), has full WPAN coordinatorcapabilities and can start a WPAN in on its own initiative for pairingand then communicating with the plurality of sensor nodes in theillustrative network.

While other communication protocols are indeed contemplated, in anexemplary embodiment, the wirelessly communicating nodes of FIG. 2incorporate the ZIGBEE RF4CE protocol. The following are generalcharacteristics of communications via ZIGBEE RF4CE:

1. Based on the 2.4 GHz PHY/MAC IEEE 802.15.4 standard.

2. Thin, flexible and future-proof networking layer is thin, flexible.

3. Co-existence with other 2.4 GHz technologies is built-in throughtechniques defined in the IEEE 802.15.4 standard and ZIGBEE RF4CE'sadvanced channel agility mechanism.

4. A simple and intuitive pairing mechanism defined for establishingcommunication links.

5. Support for multiple communication types.

6. Power management mechanism included in network layer for powerefficient implementations.

7. The standard ensures that ZIGBEE RF4CE implementations will co-exist.

8. The ZIGBEE RF4CE specification allows for both public applicationprofiles and manufacturer specific profiles or transactions.

9. Support for different applications through application layer profilesensuring device interoperability.

The following provides a technical summary of the ZIGBEE RF4CE wirelesscommunication protocol specification. The ZIGBEE RF4CE specificationdefines a simple, robust and low-cost communication network supportingwireless connectivity in a WPAN environment. The ZIGBEE RF4CEspecification enhances the functionality of the IEEE 802.15.4 standardby providing a simple networking layer and ZIGBEE Alliance developedpublic application profiles that can be used to create multi-vendorinteroperable solutions for use within WPANs. Some of thecharacteristics of a ZIGBEE RF4CE network are as follows: operation inthe 2.4 GHz frequency band according to IEEE 802.15.4, channel agilesolution operating over three channels, incorporates a power managementmechanism for all device classes, incorporates a discovery mechanismwith full application confirmation, provides a pairing mechanism withfull application confirmation, supports multiple star network topologywith inter-PAN communication, various transmission options (e.g.,uni-cast, broadcast, acknowledged, and unacknowledged, secured andun-secured), provides security key generation mechanism, utilizes anindustry standard AES-128 security scheme, supports extensions foradding manufacturer specific profiles.

With regard to network topology, an RF4CE WPAN is composed of two typesof devices (WPAN nodes): a target device and a controller device. Atarget device has full WPAN coordinator capabilities and can start anetwork on its own initiative. A controller device can join networksstarted by target devices by performing a pairing operation with atarget device. Multiple RF4CE WPANs can form a RF4CE network and devicesin the network can communicate between RF4CE WPANs. After pairing, tocommunicate with a target, a controller (e.g., sensor node in FIG. 2)first switches to the channel and assumes the WPAN identifier of thedestination RF4CE WPAN. The controller (e.g., sensor node) then uses thenetwork address assigned to the controller, previously allocated to thecontroller during pairing with the target, to identify itself on theRF4CE WPAN.

The RF4CE architecture is defined in terms of blocks and layers tosimplify specification of the protocol. Consistent with othercommunication protocol specifications, each layer of the RF4CEarchitecture is responsible for one part of the specification, offersservices to a next higher layer and utilizes services from the nextlower layer. The interfaces between the layers serve to define thelogical links that are described herein below. The layout of the layersis based on the open systems interconnection (OSI) seven-layer model.The RF4CE specification is built onto the IEEE 802.15.4 standard MAC andPHY layers and provides networking functionality and public applicationprofiles which can interface to the end user application.Manufacturer-specific extensions to public application profiles aredefined by sending vendor specific data frames within the profile. Inaddition, manufacturer-specific profiles can also be defined.

The RF4CE network layer provides two services: (1) the network layerdata service, interfacing to the network layer data entity (NLDE) and(2) the network layer management service, interfacing to the networklayer management entity (NLME). These services are accessed through thenetwork layer data entity SAP (NLDE-SAP) and the network layermanagement entity SAP (NLME-SAP). The network layer data service enablestransmitting and receiving network protocol data units (NPDUs) acrossthe MAC data service. The network layer management service permitsservice discovery, pairing, unpairing, receiver control, deviceinitialization and NIB attribute manipulation.

RF4CE devices operate in the 2.4 GHz frequency band, as specified byIEEE 802.15.4. However, to provide robust service against other commonsources of interference in this band, only a small subset of channels (3total) is used—channels 15, 20 and 25. A target device can choose tostart its network on the best available channel at startup time, and soan RF4CE network may operate over one or more of the three specifiedchannels.

RF4CE devices support channel agility across all three permittedchannels. As described above, a target device (e.g., coordinator node200 in FIG. 2) selects its own initial channel, based on the channelconditions during startup. During the course of the life of the targetdevice, channel interference may necessitate switching to anotherchannel to maintain a high quality of signal/service. Each controllerdevice paired to the target records the channel on which communicationis expected. If the target switches to another channel, the controllerdevice can attempt transmission on one of the two other channels toreacquire communications. The last channel upon which the controllercommunicated with the target is stored in the controller (sensor) nodefor a next communication attempt.

Each RF4CE device initializes according to whether the device is atarget or a controller device. A controller (e.g., a sensor transceiver)device configures the stack according to the RF4CE standard and startsoperating normally. A target (e.g., coordinator node 200 in FIG. 2)device configures the stack and then attempts to start a new WPAN. Thetarget device first performs an energy detection scan that allows it toobtain information on usage of each one of the three available channels,thereby allowing the target device to select a suitable channel on whichto initially operate. The target device then performs an active scanallowing the target device to determine the identifiers of any otherIEEE 802.15.4 WPANs operating on the selected channel, thus allowing aunique WPAN identifier to be selected for the new WPAN corresponding tothe initializing target device. The target device (e.g., coordinatornode 200) then begins operating normally.

RF4CE incorporates power saving features that allow both controllerdevices and target devices to manage power consumption by entering apower saving mode. The power saving mechanism is under the control ofeach public application profile. A device can manipulate its receiver ina number of ways: the receiver can be enabled until further notice, thereceiver can be enabled for a finite period, and the receiver can bedisabled until further notice. When the power saving mode is engaged,the receiver is enabled for an application defined duration (known asthe active period) and then disabled. This mechanism is then repeated atan application-defined interval (known as the duty cycle). Other devicescan still communicate with a device in power saving mode by targetingthe transmission during the active period. The result is a device thatperiodically enables its receiver for only a short time, allowing it toconserve power while remaining active on the network.

Turning to FIG. 3, the RF4CE network layer defines three frame types:standard data, network command and vendor specific data. Standard dataframes transport application data from public application profiles.Network command frames transport frames that allow the network layer toaccomplish certain tasks such as discovery or pairing. Vendor specificdata frames transport vendor specific application data.

The fields of the general network frame 300 format are identified inFIG. 3. A Frame control field 302 contains control information for theframe. A Frame counter field 304 contains an incrementing counter todetect duplicate frames and prevent replay attacks (security). A Profileidentifier field 306 specifies an application frame format beingtransported in the frame. A Vendor identifier field 308 specifies avalue allowing vendor extensions. A Frame payload field 310 contains theapplication frame data. A Message integrity code 312 contains a value toprovide authentication (security).

The RF4CE specification defines a number of transmission options thatcan be used by an application and combined as appropriate. Eachtransmission can be sent in a secured or un-secured mode. A transmissioncan be sent in Acknowledged mode wherein the originator data isconfirmed by the recipient. In Unacknowledged mode the originator datais not confirmed by the recipient. In Unicast mode the originator datais sent to a specific identified recipient. In Broadcast mode theoriginator data is sent to all recipients for reception and processing.In Multiple channel mode the originator attempts transmission using afrequency re-acquisition mechanism. In Single channel mode theoriginator attempts transmission on the expected channel.

With regard to discovery of other devices (nodes), a device (e.g.,coordinator 200 or sensor nodes) performs discovery in an attempt tofind other suitable devices to which the device can pair. Discovery canbe attempted repeatedly on all three channels for a fixed duration oruntil a sufficient number of responses have been received. Servicediscovery is only available to devices that are not currently in powersaving mode. During discovery, a number of pieces of information areexchanged between devices. Upon receipt by a node, the discoveryinformation is passed to the application layer which decides whether torespond.

During discovery devices exchange the following information:

Device capabilities: The type of the device (i.e. target or controller),whether the device is externally or battery powered, and level ofsecurity.

Vendor information: The RF4CE allocated vendor identifier and a freeformvendor string specifying vendor specific identification (e.g. a serialnumber).

Application information: A short user defined string which describes theapplication functionality of the device (e.g. “door sensor”), a devicetype list specifying which types of device are supported (e.g. acoordinator may list the types of sensors with which it communicates),and a profile identifier list specifying which application profiles aresupported by the device (e.g. a public application profile or amanufacturer specific profile).

Requested device type: The type of device being requested through thediscovery (e.g. a sensor may be in search of a coordinator and viceversa).

Pairing is an important aspect of devices in an RF4CE WPAN. Once asuitable device is located through discovery, a pairing link isestablished to enable communication between the two devices. Nodeswithin an RF4CE network only communicate directly with other devices onthe network if a pairing link exists.

A pairing link can be established on request from the application layerby exchanging a similar set of information as was exchanged during nodediscovery. The application on the target (e.g., coordinator 200) decideswhether to accept the pairing request and confirm the pairing requestback to the controller (e.g., sensor). Upon successful pairing, bothdevices store a pairing link in their respective pairing tables. Thisallows an originator controller to communicate with a target and thetarget to communicate back to the originator controller. Each entry inthe pairing table of the controller contains all the informationnecessary for the network layer to transmit a frame to the targetdevice. This removes the burden of addressing, etc. from the applicationlayer which can simply supply an index into the pairing table of thecontroller in order to communicate with another (target) device.

In accordance with the RF4CE protocol, each entry in the pairing table(see, FIG. 6, pairing table entry 600) contains the followinginformation: Pairing reference, Source network address, Destinationlogical channel, Destination IEEE address, Destination WPAN identifier,Destination network address, Recipient device capabilities, Recipientframe counter, and Security link key.

Security is an important aspect of many network communications. TheRF4CE specification includes a cryptographic mechanism to protecttransmissions between devices. The security specification includes thefollowing security services:

Data confidentiality: ensuring that transmitted data is disclosed onlyto the intended recipient.

Data authenticity: ensuring that the intended recipient of a ZIGBEERF4CE transmission knows that the data was sent from a trusted sourceand not modified during transmission.

Replay protection: ensuring that a secure transmission cannot simply berepeated by an attacking device if overheard.

128-bit cryptographic keys are generated by each device of a pairinglink and stored in the pairing table for future use.

Turning to the Application layer of the RF4CE, the application layer iscomposed of a profile component and an application specific component.The profile is the common aspect of a language that devices implementingthe same profile exchange to accomplish certain tasks, and allows forinteroperability between devices. The application component is providedby end manufacturers to add specific functionality to the commandsspecified through the profile. The RF4CE specification defines Alliancedeveloped public application profiles, but also permits vendors toextend public application profiles and to define completely proprietaryprofiles.

In the particular implementation of RF4CE for carrying out the sensornetwork for a refrigerated container system depicted in FIG. 2, severalfeatures of the specification are exploited. Frequency agility is usedby the coordinator 200 and sensors to avoid interference in mobileenvironments prone to highly variable noise interference. Battery lifein the sensor nodes is extended by the specified hibernation mode whichcan reduce power consumption to, for example, 1 to 10 microamps. TheWPAN range specified for RF4CE nodes are generally within the rangesrequired for refrigeration container systems (with extenders available).

Having generally described an exemplary network environment for therefrigerator control system incorporating WPAN communication network,attention is directed FIGS. 4A and 4B that depict an exemplary doorsensor assembly (e.g., door sensors 212, 214 and 216). The door sensorassembly includes a sensor and transceiver component 400 and a permanentmagnet component 402. The permanent magnet component 402 is simply anencapsulated permanent magnet with suitable physical features tofacilitate attachment to a container.

The sensor and transceiver component 400 includes, by way of example, amagnetic reed switch coupled to a data interface of an embeddedcontroller. The sensor and transceiver component 400 also includestransceiver electronics and a battery for powering the sensor andtransceiver component 400 electronics. As noted above, the sensor andtransceiver component 400 incorporates the RF4CE specification forcommunication as a controller device with a paired target (coordinator200) in a WPAN. The sensor and transceiver component 400 incorporatesthe battery power saving aspects of RF4CE described herein above as wellas back-off algorithms after several failed communications attempts toachieve an intended battery life of several (e.g., 5 years) under normalusage. The sensor and transceiver component 400 is also equipped with aset of LEDs for indicating status. By way of example, a green LEDindicates good communications status, a yellow LED indicates lostcommunications, and a red LED indicates a low battery. In the exemplaryembodiment, the reed switch and permanent magnet are configured to havean actuation distance of about 2 inches (actuated when the door isclosed).

The presence of a reed switch within the sensor and transceivercomponent 400 provides a basis for configuring the component 400 withspecification layer computer-executable instructions to supportinitiation of a pairing mode in the component 400 by swiping a magnetwithin the detection range (e.g., 2 inches) of the component 400containing the reed switch. This mode of pairing enables activation of apairing mode without use of a typical physically actuated pairingbutton. Thus, the sensor and transceiver component 400 can bemanufactured as a hermetically sealed (encapsulated) module resistant tomoisture and dust. It is noted that other magnetically actuated switchesare contemplated in place of the reed switch including Hall Effect andGiant Magneto Resistive sensors.

Given the dual use of the reed switch for sensing door state (indicatedas closed when brought within actuation range of the permanent magnetcomponent 402) and initiating pairing mode operation with thecoordinator node 200, the sensor and transceiver component 400 isconfigured at an application layer to recognize a particular magnetwave/swipe timing sequence/pattern for entering the pairing mode. Theconfigured wave/swipe timing sequence/pattern (described herein belowwith reference to FIG. 5) ensures that opening and closing the door towhich the sensor is assigned, does not unintentionally initiate thepairing mode operation of the sensor and transceiver component 400.

Turning to FIG. 5, an exemplary timing pattern is shown for initiating(i.e., causing entry into) the pairing mode of operation for thecomponent 400. In general, a pairing mode initiation sequence is definedby a sequence of timed magnet swipes (pulses, including signal rise/fallcombinations) and wait periods. The magnet swipes and wait periods fallwithin a limited overall time span or spans sufficiently long todistinguish the intentionally performed sequence from random doorchatter or other user actions that could lead to unintended entry intothe pairing mode. Referring to the sequence diagram in FIG. 5, a lowlogical signal state corresponds to when the magnetic reed switch isopen (i.e., no magnet is within range), and a high logical signal statecorresponds to when the reed switch is closed (i.e., a magnet is withinrange).

Referring to FIG. 5, the pairing state initiation sequence begins with amagnet swipe that is unlikely to arise under normal operating conditionsinvolving a person opening/closing/opening a door containing acomplementary magnet component (e.g., permanent magnet component 402).By way of example, during an “Enter Program Mode” stage, a magnet is“waved” twice across the component 400 thereby creating two logicalsignal pulses having a total elapsed time (tw) of at least 800 msec.from the first signal pulse rise to the fall of the second pulse.Alternatively, the Enter Program Mode stage is defined by a single,sufficiently slow wave of a magnet within, and then out of, range of thesensor of the component 400 to cause a signal pulse having a duration ofat least 300 msec. Longer or shorter times can be chosen for either thetwo or single pulse alternatives signaling the first stage of a sequencefor entering a pairing state in the sensor and transceiver component400. However, too short of a time will potentially cause confusion witha door chatter movement.

Continuing the description of the illustrative pairing state initiationsequence, the falling edge of the signal, marking the end of the EnterProgram Mode stage, marks a beginning of a Silence Period 1 stage havinga duration (ts1). During the Silence Period 1 stage there is no reedswitch activation. The duration of the Silence Period 1 stage is, forexample, 2 seconds. However, other silence periods can be specified(e.g., greater periods of silence).

A Pairing Mode Confirmation Period stage commences immediately uponcompleting the mandated wait period (e.g., 2 seconds) for the SilencePeriod 1 stage. During the Pairing Mode Confirmation Period stage adesignated quantity of swipes (waves of a magnet within range of theswitch within the component 400) are completed during an elapsedconfirmation period having a duration (tc1) that meets a prescribed timelimit (e.g., 10 seconds). In the illustrative example, three swipes of amagnet—each swipe (pulse) having a duration (tp) of at least 300 msec.(to be counted)—must be completed within the prescribed time limit tocomplete the Pairing Mode Confirmation Period stage. Alternatively, moreor fewer magnet swipes are required (e.g., 2 swipes, 4 swipes) tocomplete this stage. After the user performs the three required swipeswithin the prescribed (10 second) time period, the pairing modeinitiation sequence mandates completion of a second silence period(ts2)—Silence Period 2—having a duration of, for example, at least 2seconds. Upon completing the Silence Period 2 stage, the component 400initiates pairing with the coordinator 200 for the WPAN.

Moreover, in a further enhancement to the above-described pairing modeinitiation procedure, the various stages of the pairing state initiationsequence are visually indicated by the component 400, for example, usingvarious colored light-emitting diodes (LEDs). The LEDs (e.g., green,yellow and red) are employed to guide a user through the various stagesof the pairing mode initiation sequence. For example, during the SilencePeriod 1 stage and Silence Period 2 stage, a yellow LED flashes for theduration of the stage—an indication to the user to use caution to ensurethat a magnet field source does not enter the range of the component400's magnetic field sensor (e.g., reed switch). Thereafter, during thePairing Mode Confirmation Period, a green LED flashes to indicate whenthe user should commence/perform a series of (three) confirmatory magnetswipes. For, example, the multiple swipe Pairing Mode ConfirmationPeriod stage is successfully completed when the series of LED flashes isfollowed by corresponding swipes within a designated period.Furthermore, another LED signal pattern indicates when pairing mode isinitiated at the end of the sequence depicted in FIG. 5 and when thepairing of the controller 400 with the coordinator 200 is successfullycompleted. There are, of course, many different patterns that can beused to ensure that pairing is limited to intended occasions. The aboveexample, and other suitable sequences, balances the need to avoidunintended pairing attempts and making the sequence sufficientlybrief/simple to ensure user compliance.

Another aspect of pairing a sensor node with a coordinator node in aWPAN environment is the unintended pairing of a sensor with multiplecoordinators. In the context of refrigerated container systems, suchunintended pairing arises when a sensor is paired while in a depotcontaining several other coordinators that are capable of pairing withthe sensor. The unintentionally paired coordinator (target device)eventually leaves the vicinity of the sensor, yet the inadvertentlyentered entry remains in the sensor's pairing table (see e.g., FIG. 6,pairing table entry 600). The pairing table entry fields identified inFIG. 6 are known to those familiar with the ZIGBEE RF4CE standard, andthus will not be described in detail herein since the point of thecurrent disclosure is to identify a suitable environment for carryingout the pairing table cleaning method described herein. Furthermore,while such extra pairing table entry (or entries) is easily accommodatedin the plentiful memory space of the sensor's controller electronics,the presence of the additional entry potentially results in unnecessarywireless message transmissions by a sensor node in search of acoordinator that is no longer in range. Such searching imposes anunnecessary and excessive drain on the sensor's battery power, therebypotentially substantially shortening the sensor node battery lifespan.Another source of unwanted pairing table entries arises from replacementof previously paired (malfunctioning) coordinator (target device) by anew coordinator. In such case, when the new target device is paired anda new pairing table entry is created, the old pairing table entryremains in the pairing table of the sensor node.

A method is described, with reference to FIG. 7A, for clearing erroneouspairing table entries from RF4CE WPAN devices without user intervention.The method relies upon additional logic relating to a connection processwhereby a sensor establishes a connection to a coordination listed inthe pairing table of the sensor implementing the RF4CE WPAN protocol.During step 700, a sensor (controller device), such as the door sensor212 in FIG. 2, encounters a failure to establish a connection “event”with a coordinator (target device) to which the sensor had previouslypaired. Such failure to connect with a coordinator listed within thesensor's pairing table can arise under any of several circumstances,including: the temporary shutdown of the coordinator, thefailure/replacement of the coordinator, or the inadvertent pairing witha nearby foreign WPAN (described above) when the sensor device wasinitially paired with its intended coordinator (e.g., coordinator 200).

Thereafter, during step 702, the sensor determines whether thenon-responding coordinator is the only device identified in the sensor'spairing table. If the non-responding coordinator is the only entry, thencontrol passes to the End. Such event is possibly just a temporarilynon-responsive coordinator. Step 702 is inserted as a failsafe to ensurethat the sensor maintains at least one entry in the sensor's pairingtable. However, if more than one entry is present in the pairing table,then control passes from step 702 to step 704.

At step 704 the sensor repeatedly attempts to establish a connectionwith the non-responsive coordinator over an extended period (e.g., anhour). If at any point the sensor is able to establish a connection,then control passes to the END. However, if the failures to connectcontinue repeatedly for the duration of the multiple re-tries over theextended period, then control passes to step 706 wherein the sensorpurges the entry corresponding to the non-responsive coordinator fromthe sensor's pairing table. Control then passes from step 706 to theEND. As such, a self-healing procedure is provided for both instancesdescribed above when a previously paired coordinator is no longer partof an intended WPAN to which a sensor belongs.

A failure detection definition implemented during step 704 differs inaccordance with various exemplary embodiments. In one particular examplefailure is noted when 50 repeated connection attempt failures arerecorded for the sensor during a period of four hours. The frequency ofattempts can vary over the maximum wait period before a final connectionfailure is established during step 704. In yet another example, thesensor executes a tiered failure approach wherein each tier specifies adifferent combination of wait period (between connection attempts) andtotal number of attempts. In a particular example of a tiered failureapproach, a frequency of attempts decreases (i.e., a wait period betweenattempts increases) and the total number of failed attempts (beforemoving to a next connection failure tier) decreases. Even moreparticularly, the tier number itself is used to exponentially increasethe wait (e.g., double the wait period between attempts for each tierincrease) and exponentially decrease the total number of attempts (e.g.,halve the number of attempts) for each tier. This approach has theadvantage of covering a wider variety of potential “temporary” failureswhile ensuring that truly erroneous table entries are eventually purgedfrom the table—potentially after a several day wait—to accommodate asituation such as maintenance operations that are disrupted over aweekend.

Similarly, with reference to FIGS. 7B and 7C, steps can be taken at thecoordinator 200 to ensure against improper pairing of a sensor(controller device) from another refrigerated container system in anarea proximate the coordinator. Referring to the summarized operation ofthe coordinator, during step 720 the coordinator node receives a pairingrequest message from a sensor node seeking to pair with the coordinatornode in a WPAN. The pairing request message contains a wealth ofinformation that can be used to filter requests. Moreover, varioustiming/signal strength/query-response requirements can be imposed on topof the basic message format requirements. Such requirements, imposed bythe coordinator prior to allowing a pairing operation are discussedherein below.

During step 722 the coordinator extracts one or more property valuesfrom the pairing request message. Such extraction can include theaforementioned measures relating to message information as well as thetime/signal strength/query-response requirements mentioned herein.

During step 724 the coordinator filters the pairing request informationextracted during step 722 against stored filter values and pairingrequest criteria (including data/procedural requirements). Control thenpasses to step 726.

During step 726, responsive to the test(s) applied during step 724, ifthe provided property value(s) meet a property filter/pairing criteria,then control passes to step 728 wherein the coordinator commencesoperations for pairing with the requesting wireless sensor node.Otherwise, if the provided property value(s) and/or some other propertyfilter/pairing criteria are not met, then control passes from step 726to step 729 wherein the pairing request is rejected through eitherexplicit response or passive non-response by the coordinator node.

By way of example, and with reference to FIG. 7B, during step 724 thecoordinator 200 utilizes detailed knowledge of the properties of aspecific wireless network to prevent inappropriate pairing requests. Ina first manner of preventing improper pairing, identified in the tableof FIG. 7B, the coordinator 200 filters requests based upon propertiesidentified in the pairing request from a sensor. Such propertiesinclude: vendor string, vendor ID, user string, and MAC address (e.g.,apply address to an expected range or the Organizationally UniqueIdentifier contained in first 3 bytes of the MAC address). Yet otherapplication level requirements are incorporated into the coordinator200's pairing protocols that require, for example:

1. A particular switch sequence from the requesting sensor.

2. A challenge-response sequence with visual or auditory prompts todetermine with high confidence that a person is activating the switchand it is not an accidental occurrence.

3. Use of an external device as a tool to generate a pairing requestsignal which would be detected by a sensor device via optical,electrical or magnetic communication.

4. Use a mechanical switch cover to prevent accidental pressing.

5. Locate the pairing button within a recess that cannot easily bereached.

Link quality indication (LQI) is also used by the coordinator 200 toreject week signals from likely distant sources that are not intendedmembers of the coordinator 200's WPAN. Still another way to lessen thechance of inadvertent pairing is for the coordinator 200 to monitor aquantity of commissioning attempts over time, and throttle excessivepairing attempts arising from non-intended or inappropriate use of apairing button. The throttling is intended to reduce a probability thatrandom switch activations on a sensor node will initiate a pairingrequest with one or more coordinator nodes within the vicinity of thesensor node. Moreover, the above-described tools used by a coordinator200 to prevent unintentional pairing between closely situated containersystems or other WPANs, can be combined such that one or all of theabove potential methods are used to block unintended pairings.

Yet another potential draw upon a sensor's limited battery power supplyis excessive signal processing occurring due to door chatter arisingfrom, for example, an improperly secured door. Such situations result intransient open/close door signals being registered. In each instancewhere the door opens sufficiently, an interrupt issues and the sensorwakes up to register and report the event. To avoid unnecessary wakingup of the door sensor (e.g., door sensor 212), a procedure isimplemented by logic executed within the sensor electronics. The logic,summarized in FIG. 9, causes the sensor to disable sensor interrupt (andassociated routine) during step 902 after detecting excessive doorchatter during step 900 (i.e., a number of door status changes within atime period that exceeds a specified limit. Disabling the sensorinterrupt causes the sensor electronics to ignore the door signal bytemporarily preventing executing the sensor interrupt routine when thesensor changes state. Moreover, during step 904 the sensor issues anotification message (alarm) to the coordinator that, in turn, signalsthe operator to attend to the door that is causing the unstable(chattering) sensor signal.

Thereafter, during step 906 the sensor electronics periodically monitorthe door status (under control of a watchdog timer that expires everyminute while awaiting a determination that the door sensor status hasreached a stable open/closed state. During step 908, if the sensorelectronics determine that the signal stabilized at a constant open orclosed status for a period of time (as evidenced by the door signalstate registered upon expiration of the watchdog timer during a periodwhile the sensor interrupt is disabled) then control passes to step 910.During step 910 the door sensor signal interrupt is enabled to resumenormal sensor signal operation. Otherwise, if during step 908 theperiodic reading of the sensor signal over a period of time indicatesthat the sensor state has not stabilized, then control returns to step906.

Turning to FIGS. 8A and 8B, exemplary timing diagrams depict the actualsignal sensed by the door sensor (e.g., door sensor 212) duringoperation of the refrigerated container system. In FIG. 8A, a door ischattering and is not secured. The chatter signal, as indicated by thedirection of the arrows, causes the sensor to repeatedly wake, observethe door status, and issue a message to the coordinator at least 20times (by way of example) during a period of time period t1 that is lessthan a specified time window (e.g., 5 minutes). After the sensorinterrupt is activated the twentieth time during the period of time t1(less than for example 5 minutes), at time td, a power saving featurecauses the sensor to disable the sensor event interrupt. Thus, thesensor electronics ignore the frequent open/close door event signal forthe remainder of the sequence depicted in FIG. 8A. However, after timet1 (e.g., after the twentieth transition in under 5 minutes), the doorsensor enables a watchdog timer that wakes up the sensor electronicsevery minute (or other configured wait period) to monitor the status ofthe door status signal (shown by the vertical up/down arrows). Thesensor readings that are actually processed by the sensor (uponexpiration of the watchdog timer) are indicated by the bold arrows. Thedashed arrows indicate sensor transitions that are not processed by thesensor electronics.

A second feature of a door chatter signal handling scheme implemented bythe sensor electronics relates to recovery from the state where thesensor interrupt is disabled (and the watchdog is enabled). As notedabove, when the sensor interrupt is disabled, an alarm message isforwarded by the coordinator to a controller that, in turn, issues analarm to an operator. In FIG. 8B, the door is subsequently secured (inresponse to the alarm). However, the sensor electronics do notimmediately enable the door status interrupt. Instead, the watchdogtimer interrupt remains enabled for a period of time wherein the doorsensor signal status is read once every minute (or other configured waitperiod). After periodically waking up (under watchdog timernotification) and reading a same door sensor status value (e.g., closed)multiple times (e.g., 7 times) over several minutes, the sensorelectronics re-enable the previously disabled door sensor interrupt (attime to in FIG. 8B) and disable the watchdog timer. At this point, theinterrupts are operating in the normal operational state.

Embodiments of the invention are described herein. Variations of thoseembodiments may become apparent to those of ordinary skill in the artupon reading the foregoing description. The inventors expect skilledartisans to employ such variations as appropriate, and the inventorsintend for the invention to be practiced otherwise than as specificallydescribed herein. Accordingly, this invention includes all modificationsand equivalents of the subject matter recited in the claims appendedhereto as permitted by applicable law. Moreover, any combination of theabove-described elements in all possible variations thereof isencompassed by the invention unless otherwise indicated herein orotherwise clearly contradicted by context.

What is claimed is:
 1. A method of managing a wireless door sensor toavoid excessive sensor signal processing arising from a chattering doorsensor signal stream, the method comprising: detecting, by the wirelessdoor sensor, a specified number of door transitions within a specifiedtime period, and in response to said detecting: disabling a door signaltransition event processing routine; enabling a timer-based door sensorsignal processing routine, wherein the timer-based routine reads a doorsensor signal status regardless of whether a door signal transition hasoccurred, and re-enabling the door signal transition event processingroutine in response to reading a same value for the door sensor signalstatus multiple times over a time duration, such multiple readings beingindicative of the door position being stabilized.
 2. The method of claim1 wherein the wireless door sensor is a wireless sensor node within awireless personal area network (WPAN).
 3. The method of claim 2 whereinthe WPAN is incorporated into a transportable refrigerated containersystem (“reefer”).
 4. The method of claim 2 wherein the wirelesspersonal area network implements communication between a coordinator andthe wireless sensor node according to a ZIGBEE RF4CE wireless personalarea network communication protocol.
 5. The method of claim 1 whereinwireless door sensor includes a switch.
 6. The method of claim 5 whereinthe switch is a magnetic switch.
 7. A wireless door sensor node forincorporation into a wireless personal area network, the wireless doorsensor node including: a switch facilitating generating a door sensorstatus signal; a processor; and a non-transitory computer readablemedium including computer-executable instructions, executable by theprocessor, for managing the wireless door sensor node to avoid excessivesensor signal processing arising from a chattering door sensor signalstream, the method comprising: detecting, by the wireless door sensor, aspecified number of door transitions within a specified time period, andin response to said detecting: disabling a door signal transition eventprocessing routine, enabling a timer-based door sensor signal processingroutine, wherein the timer-based routine reads a door sensor signalstatus regardless of whether a door signal transition has occurred, andre-enabling the door signal transition event processing routine inresponse to reading a same value for the door sensor signal statusmultiple times over a time duration, such multiple readings beingindicative of the door position being stabilized.
 8. The wireless sensornode of claim 7 wherein the sensor is configured to sense a change inmagnetic field in response to a change in an open/closed status of adoor.
 9. A transportable refrigerated container system including: arefrigeration system including a controller; a wireless communicationsystem configured as a wireless personal area network (WPAN), the WPANcomprising: a wireless sensor node, configured to sense a status of adoor in the refrigeration system and communicate the status of the doorto a second node within the WPAN, the wireless sensor node comprising: aswitch facilitating generating a sensor status signal indicating thestatus of the door; a processor; and a non-transitory computer readablemedium including computer-executable instructions, executable by theprocessor, for managing the wireless door sensor node to avoid excessivesensor signal processing arising from a chattering door sensor signalstream, the method comprising: detecting, by the wireless door sensor, aspecified number of door transitions within a specified time period, andin response to said detecting:  disabling a door signal transition eventprocessing routine,  enabling a timer-based door sensor signalprocessing routine, wherein the timer-based routine reads a door sensorsignal status regardless of whether a door signal transition hasoccurred, and re-enabling the door signal transition event processingroutine in response to reading a same value for the door sensor signalstatus multiple times over a time duration, such multiple readings beingindicative of the door position being stabilized.